Terror birds were the biggest birds the world has ever seen, and the new species is by far the largest terror bird yet, says paleontologist Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles County, California.

"Some of these birds had skulls that were two and a half feet [almost a meter] in length. [They] were colossal animals," he said.

The new, currently unnamed species stood about ten feet (three meters) tall and had a head as big as that of a horse.

The largest terror birds could likely swallow dog-size prey in a single gulp, experts say.

The bird's most striking feature—literally—was its giant nose, a roughly 18-inch (46-centimeter) beak with a sharp, curving hook shaped like an eagle's beak.

Whether the flightless birds used their beaks to impale or bludgeon their prey is unknown, Chiappe says. But a single hit from their "massive skull[s] would have killed anything immediately."

Intact Skull

Terror birds were first discovered in the late 1800s and are believed to have become South America's top predators after the dinosaurs died off 65 million years ago.

A high school student unearthed the ancient remains of the new species three years ago in the Patagonia region of Argentina (see photos of Patagonia).

Chiappe and his colleagues examined the specimens and found that the fossils—a well-preserved skull and foot bones—are about 15 million years old.